1. Field of the Invention
The present invention relates to a disk drive device and particularly to the structure of a disk drive device.
2. Description of the Related Art
In recent years, there have been major improvements in the structural strength of disk drive devices. Particularly, the strength of the shaft bearing units of disk drive devices, such as hard disk drives (HDD), have greatly improved due to the utilization of fluid dynamic bearings (FDB). Moreover, as mobile devices are becoming more prevalent, the disk drives in mobile devices are being developed with essential properties, such as larger storage capacity, with increased thinness in the disk drive, and with improvements in impact resistance. These developments are essential in order to make the disk drive more portable and appropriate for mobile devices. Such improvements have been widely known, and have been already known to be applied to HDD. For example, see Japanese Patent Laid-Open No. 2007-198555, which discloses a disk drive device that enables an HDD containing a memory disk with a 63.5 mm outer diameter, the structure of the HDD having a thickness of 9 mm.
To satisfy this demand for creating a disk drive with high-capacity storage, it is required to have the recording disk to be installed on the mounting hub of the disk drive device so that it is stable when driven in a rotational manner. In order to do this, one needs to minimize the axial runout at the mounting point of the memory disk. If the axial runout of the mounting area where the recording disk meets the hub is excessive, this motion creates a large deviation along the axis of rotation of the recording disk, causing the magnetic head, which reads/writes magnetic data from/to the recording disk, to lose tracking ability (going “off track”).
In the scenario where the axial runout is very large, the normal functions of reading and writing magnetic data are impaired. This challenge must be overcome when creating a disk drive with high-capacity storage.
Moreover, in order to meet the demand for the disk drive with increased overall thinness, the hub inside of the disk drive must also be made thinner. However, when the hub becomes thinner, the strength and stability of the hub is lowered. When manufacturing the hub, the lathing process (or chucking process) holds the hub in place in order to cut the form of the hub. In doing so, the place where the hub comes in contact with the lathing process is exposed to contact pressure. The lowering of the hub strength creates warping over the overall intended shape of the hub due to this contact pressure. The thinner the hub becomes, the more susceptible it is to warping, which, in turn, lowers the processing accuracy.
The thinning of the hub also leads to the weakening of the strength of the meeting point at which the disk drive's hub meets the shaft. In situations when an unequal weight distribution is applied to the hub, such as during motion shock, the force of impact is focused at the meeting point, making the shape of the hub change and creating a deviation in the axis of rotation that causes the axial runout to worsen. This additional challenge must be overcome when also creating a disk drive that has increased thinness.